Effect of Ammonium Enrichment on Respiration, Zooxanthellar Densities, and Pigment Concentrations in Two Species of Hawaiian Corals

Abstract

Small branch tips or "nubbins" of two species of Hawaiian corals, Pocillopora damicornis (Linnaeus) and Montipora verrucosa Vaughan, were exposed to four ammonium concentrations, ammonium-stripped < 2 uM), ambient (~2 uM), and two enriched (20 uM and 50 uM) in microcosm tanks. Nubbins represent replicates of a single coral colony. We examined the effect of ammonium enrichment on zooxanthellar densities, pigment concentrations, and respiration rates of the nubbins. Nubbins of both P. damicornis and M. verrucosa showed a trend of increased pigment concentration with elevated ammonium concentration. Pocillopora damicornis increased from 9.3 ug chlorophyll a cm-2 in the ammonium-stripped treatment to 24.8 ug cm-2 in the 50-uM ammonium treatment. Similarly, M. verrucosa increased from 1.9 to 19.4 ug chlorophyll a cm-2. There were no significant differences in algal densities, pigment concentrations per cell, pigment ratios, or respiration rates.